The present invention relates to reflective micromirrors and micromirror array devices for, e.g., projection-type displays, for steering light beams, maskless lithography, maskless micro-array production, etc. A common feature is a micromirror that is movable so as to deflect incident light. In one type of conventional direct view or projection-type display system, an array of reflective micro-mirrors is provided for producing an image. Typically the micromirrors have either a tilt angle for the “ON” state and a non-deflected state for the “OFF” state, or the same tilt angles for “ON” and “OFF” states but with opposite sign.
As an exemplary application for displaying an image, a micromirror is associated with a pixel of an image. At a time when the pixel is “bright”, a micromirror is set to the “ON” state. Incident light is reflected by the micromirror into a cone of reflected light towards the projection lens or the display target. At another time when the pixel turns to “dark”, the micromirror is set to the “OFF” state. Incident light is reflected into another cone of reflected light away from the projection lens and the display target. However, when the cone of the reflected light by the micromirror in the ON state and the cone of the reflected by the micromirror in the OFF state are too close, e.g., the angle between the two light cones is too small, the two light cones may be overlapped. The contrast ratio of the pixel, thus the quality of the displayed image is reduced (contrast ratio is the ratio of luminance between the brightest white that can be produced and the darkest black that can be produced). And it is a major determinant of perceived image quality. If a displayed image has high contrast ratio, a viewer will judge it to be sharper than a displayed image with lower contrast ratio, even if the lower contrast image has substantially more measurable resolution. The degradation of the contrast ratio becomes larger as the angular extent of the incident beam grows.
Therefore, what is needed is a spatial light modulator that has a high resolution, a high fill factor and a high contrast ratio. What is further needed is a spatial light modulator that does not require polarized light, hence is optically efficient and mechanically robust.